Focussing system for an electron beam incorporating axially magnetized annular magnets



June 1955 J BRETTING ETAL 3,188,533

FOCUSSING SYSTEM FOR AN ELECTRON BEAM INCORPORATING AXIALLY MAGNETIZEDANNULAR MAGNETS Filed Feb. 18, 1963 5 Sheets-Sheet 1 Fig.7

UORK .ZBRETTING Hans-30mm GRIEM Jnvenfars Rbtovnegs June 1965 J.BRETTING ETAL 3,188,533

FOCUSSING SYSTEM FOR AN ELECTRON BEAM INCORPORATING AXIALLY MAGNETIZEDANNULAR MAGNETS Filed Feb. 18, 1963 asheets-Sheet 2 UORK LBRETTINGHFINS- sbneeu GRiEm Jnrenfors nttovness June 8, 1965 J. BRETTING ETAL3,188,533

FOCUSSING SYSTEM FOR AN ELECTRON BEAM INCORPORATING AXIALLY MAGNETIZEDANNULAR MAGNETS 3 Sheets-Sheet 3 Filed Feb. 18, 1963 tsoRK IBRETTINGanus-30mm Gmem Jnrenzars HttovnegS United States Patent Ofiice 3,188,533Patented June 8, 1965 3,188,533 FOCUSSING SYSTEM FOR AN ELECTRON BEAMINCORPORATING AXIALLY MAGNETIZED AN- 14 Claims. (a. 317-200 The presentinvention relates to a system for focussing an electron beam within avacuum envelope, which focussing system comprises a plurality ofcoaxially arranged annular magnets, there being ferromagnetic pole shoesof different polarity arranged between alternate pairs of successivemagnets. Such a focussing system is particularly adapted for use intravelling-wave tubes.

It is known to focus an electron beam, for example in a travelling-wavetube, by means of so-called periodic magnetic focussing systems. Suchfocussing systems generally consist of several permanent magnet rings orelectromagnetic coils which surround the tube and are arrange-d next toeach other, with consecutive magnets having opposing magneticpolarities.

It is also known, in such periodic focussing systems, to provideferromagnetic annular discs between the individual magnets, that is tosay, for example, between the individual magnet rings which aremagnetized in axial direction, which ferromagnetc annular discs arefashioned as pole shoes which surround the tube.

One difficulty with the above-described periodic magnetic focussingsystems, is that the magnetic characteristics of the individual partsthereof, i.e., the actual magnets and the pole shoes arrangedtherebetween, will fluctuate beyond acceptable tolerances. Consequently,the amplitude and position of the magnetic focussing field within thetube will fluctuate beyond acceptable limits. The disturbance of themagnetic field is particularly marked if, for example, all or part of amagnet is omitted between two pole shoes, as is sometimes necessary if,for' instance, a wave guide for coupling high frequency energy to ordecoupling such energy from the tube has to pass through the focussingsystem.

It is, therefore, an object of the present invention to provide afocussing system which overcomes the above drawbacks, namely, afocussing system by means of which a more homogeneous focussing field isproduced. According to the present invention, this is accomplished byinterconnecting the poleshoes of like polarity with at least oneferromagnetic yoke. Consequently, the magnetic potential between eachtwo adjacent pole shoes of different polarity will be the same. Thebalancing effect of the ferromagnetic yokes according to the presentinvention is sufiiciently large so that an appreciable disturbance ofthe focussing field is avoided even if one or more magnets is omitted soas to allow one or more wave guides to be connected to thetravelling-wave tube. Each yoke is, in practice, made of a material ofhigh permeability having a sutficiently high saturation field strength.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a sectional view of one embodiment of a focussing systemaccording to the present invention.

FIGURE 1a is a perspective view of a pole shoe according to the presentinvention, there also being shown a web for connecting the actual poleshoe portion with the yoke.

FIGURE 2 is a plan view of another embodiment of a focussing systemaccording to the present invention in which each pole shoe has two websby which it is connected to yokes.

FIGURE 2a is a perspective view of a section of the structure shown inFIGURE 2.

FIGURE 3 is a sectional view of a focussing-system according to thepresent invention in which a coupling line is provided.

FIGURE 4 is a perspective View showing the interposition of a couplingline.

Referring now to the drawings and to FIGURES l and la thereof inparticular, the same show a focussing system for focussing an electronbeam within a vacuum envelope V, the focussing system comprising anumber of magnet means constituted by axially magnetized, coaxiallyarranged and spaced-apart ring magnets 1 of alternating polarity, i.e.,each magnet (except the end magnets) has a N-pole directed toward aN-pole of one adjacent magnet and a S-pole directed toward a S-pole ofthe other adjacent magnet. Pole shoes 2 are arranged between the ringmagnets. Each pole shoe has a web 3, the position of the Webs 3 being soselected that they join one of two yokes 4 and 5; as shown in FIGURE 1,each of the pole shoes interposed between two N-poles has its webconnected to yoke 4 while each of the pole shoes interposed between twoS-poles has its web connected to yoke 5.

The pole shoes can be fashioned in any desired manner. In the embodimentillustrated in FIGURES 1 and la, each pole shoe has at its innerperiphery an enlarged pole shoe portion surface 6 and two laterallyextending flanges 7 (FIGURE 1a); in this way, the ring magnets 1 maysimply be slipped over the flanges so that the pole shoes serve also asthe mechanical mounting means for holding the ring magnets in place.There can be as many webs per pole shoe as desired; in the illustratedembodiment, there is but one web for each pole shoe and the arrangementof the parts in such that the webs of pole shoes of dillerent polarityare diametrically opposite each other.

If desired, one or more ring magnets can be'omitted, for example the twoend rings, so as to accommodate hollow wave guides by means of which thetravelling-wave tube is coupled to another component, such as a sourceof high-frequency energy.

In the embodiment of FIGURES 2 and 2a, the pole shoes are in the form ofrectangular plates 21 provided with an opening 22 through which isinserted the tube that is to be focussed. The pole shoes 21 and 23,shown as being angularly displaced by represent pole shoes of oppositepolarity. Arranged between the pole shoes 21, 23, is an annular magnet24 constituted, in the instant embodiment, by an electromagnetic coil.The webs of pole shoes 23 (only one of which is illustrated) areconnected by two diametrically opposite yokes 25 while the webs of thepole shoes 21 (of which, likewise, only one is shown) are connected bytwo diametrically opposite yokes 25. In the illustrated embodiment, theyokes 25 and 26, which are preferably plate members of rectangular crosssection, also serve as a screening means for the entire magnetic system.

The ferromagnetic yoke means will generally be arranged exteriorly ofthe outer periphery of the magnets, as shown in the above-described twoembodiments. The invention has been found to be particularlyadvantageous when the magnets are axially magnetized permanent magnets.The pole shoes between the magnets can be of any suitable configuration.The pole shoes are connected with their respective yokes by means offerromagnetic webs which are at least magnetically connected with thepole shoes.

In the embodiment of FIGURE 3, the focussing system comprises magnets 35and 38 arranged with alternate illustrated. The outer periphery of therings engages the yoke or yokes 34; as shown in FIGURE 3, the outer periphery of the radially magnetized ring is a N-pole, as are the yokes34, so that the outer periphery of ring 32 isin contact with a yoke oflike polarity. The inner periphery of the ring 32 is providedwith a poleshoe ring 39. The space between the radially magnetized ring 32 and thelast pole shoe ring 37, which otherwise would be occupied by anotheraxially magnetized ring magnet, is here shown as being occupied by ahollow conductor 31 by means of which high-frequency energy is coupledto the tube to be focussed. The radially magnetized ring thus takesover, to a certain extent, the function of a pole shoe. The in- A (e)second yoke means magnetically connecting said set of second pole shoesto each other. 2. A focussing system as definedin claim 1 wherein eachof said magnet means comprises an electromagnetic coil.

' 3. A focussing system as defined in claim ll wherein each of saidmagnet means comprises a permanent magnet. 4. A focussing system asdefined in claim 1 wherein said pole shoes encompass the vacuumenvelope.

5. A focussing system as defined in claim 1 wherein said pole shoescomprise a pole shoe portion and at least one web for connecting therespective pole shoe portion with the respective yoke means.

6. A focussing system as defined in claim 5 wherein said two yoke meansare arranged diametrically opposite each other.

7. A focussing'system as defined in claim 1 wherein each of said yokemeans comprises two yokes, and wherein each of said pole shoes comprisesa pole shoe portion tensity of this ring 32. can, for purposes ofcontrolling the focussing field, be regulated by means of a magneticshunt 33 which is made, for example, of a ferromagnetic annular disc.The shunt 33 will be suitably supported, e.g., by a plastic ring 33ainterposed between the shunt and the yokes 34.

FIGURE 4 shows a hollow conductor 47 arranged next to a pole shoe 41provided with a web 43. The pole shoe is fashioned as shown in FIGURE1a, except that it has a flange 7 only on that side which faces awayfrom the hollow conductor 47, thereby to leave space for the conductor.The diametrically opposite yokes 44 and 45 are of different polarity. Ofthe permanent ring magnets, only magnet 42 is visible.

and two webs for connecting the respective pole shoe portion with thetwo yokes. of the respective yoke means. 8. A focussing system asdefined in claim 7 wherein the two yokes of each yoke means are arrangeddiametrically opposite each other, said first and second yokemeansbeingdisplaced 90 relative to each other. I a 9. A focussing system asdefined in claim 8 wherein each of the four yokes comprise a platemember, said four plate members as a whole serving as a screening means9 for the entire magnetic system.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

What is claimed is:

1. For use with a vacuum envelope, a system for focussing an electronbeam within the envelope, said focussing system comprising, incombination:

(a) a plurality of coaxially aligned and spaced-apart annular magnetmeans each having axially spacedapart N and S poles, said magnet meansbeing arranged so that any one magnet means has its N-pole directedtoward the N-pole of an adjacent magnet means and its S-pole directedtoward the S pole of an adjacent magnet means;

(b) a set of first pole shoes each interposed between two respectivefacing N-poles;

(c) a set of second pole shoes each interposedbetween two respectivefacing s-poles;

(d) first yoke means magnetically connecting said set of first poleshoes to each other; and

it A focussing system as defined in claim 1 wherein said focussingsystem further comprises'two radially magnetized permanent ring magnetsarranged coaxially with said set of magnet means; said ring magnetsbeing located adjacent the first and the last of said set of magnetmeans,

respectively; the outer periphery of eachof said ring magnets beingmagnetically connected with the particular yoke which is of the samepolarity as the respective outer periphery.

' 11. A focussing system as defined in claim 10 wherein a high-frequencycoupling line is arranged between one of said ring magnets and thenearest of said magnet means. 12. A focussing system as defined in claim10 wherein said focussing system further comprises magnetic shunt meansarranged adjacent said ring magnets.

13. A focussing system as defined in clalm 1 wherein said pole shoescomprise means for holding said magnet means.

14. A focussing system as'defined in claim 13 wherein said holding meanscomprise annular flanges integral with said pole shoes, said magnetmeans being permanent magnet rings which encompass said flanges so as tobe held thereby.

References Cited by the Examiner UNITED STATES PATENTS V S JOHN F.BURNS, Primary Examiner.

1. FOR USE WITH A VACUUM ENVELOPE, A SYSTEM FOR FOCUSSING AN ELECTRONBEAM WITHIN THE ENVELOPE, SAID FOCUSSING SYSTEM COMPRISING, INCOMBINATION: (A) A PLURALITY OF COAXIALLY ALIGNED AND SPACED-APARTANNULAR MAGNET MEANS EACH HAVING AXIALLY SPACEDAPART N AND S POLES, SAIDMAGNET MEANS BEING ARRANGED TO TH AT ANY ONE MAGNET MEANS HAS ITS N-POLEDIRECTED TOWARD THE N-POLE OF AN ADJACENT MAGNET MEANS AND ITS S-POLEDIRECTED TOWARD THE S-POLE OF AN ADJACENT MAGNET MEANS; (B) A SET OFFIRST POLE SHOES EACH INTERPOSED BETWEEN TO RESPECTIVE FACING N-POLES;(C) A SET OF SECOND POLE SHOES EACH INTERPOSED BETWEEN TWO RESPECTIVEFACING S-POLES; (D) FIRST YOKE MEANS MECHANICALLY CONNECTING SAID SET OFFIRST SHOE TO EACH OTHER; AND (E) SECOND YOKE MEANS MECHANICALLYCONNECTING SAID SET OF SECOND POLE SHOES OF EACH OTHER.